Giardia lamblia is a flagellated protozoan parasite which is a common cause of diarrhea in many countries throughout the world. Its life cycle consists of two stages, the trophozoite and the cyst. The trophozoite replicates in the small intestine and can cause disease in the susceptible host. Trophozoites are not usually found except in liquid stools of patients with diarrhea or upon purgation. When present, they exhibit motility that resembles Brownian motion in water. When a purgative is used, some trophozoites become inactive. They can encyst in the small intestine and are excreted in the feces. Other hosts are subsequently infected by ingestion of these cysts.
Giardia lamblia produces giardiasis and lives high in the intestinal tract. Considerable clinical evidence suggests that the trophozoites may be capable of producing inflammatory changes in the itestinal wall. Trophozoites of this parasite may be recovered in duodenal drainage or from the gall bladder. Proof of its primary role in gastrointestinal disease is available (Hoskins, L. C., et al., Gastroenterology, 53: 265-268 (1967); Morbidity and Mortality, Weekly Report, Center for Disease Control 19 (47): 455-459 (1970)).
The most commonly used method for diagnosing giardiasis is the identification of Giardia lamblia cysts or trophozoites in stools by histological staining techniques using Lugol's solution, merthiodate-iodine-formaldehyde or trichrome. These methods are time consuming, tedious and insensitive. A number of rapid laboratory methods have become available. A detection method with increased specificity would be valuable to clinicians because it would make it possible to differentiate Giardia lamblia from other organisms present in a sample being analyzed.